Inhibition of wet strength resin deposition in papermaking felts

Abstract: This invention relates to an improved press felt conditioning treatment which controls the deposition of poly(amino-amide) - epichlorohydrin type resins in a press felt. The treatment comprises applying to the felt an effective inhibiting amount of a conditioner consisting of: an ethoxylated nonylphenol having greater than about 30 moles of ethoxylation; sodium n-hexadecyl diphenyloxide disulfonate; a fatty acid imidazoline or an alkylamidopropyldimethylamine which include an alkyl hydrophobe substituent having a carbon chain length of about 18.

Description: The present invention relates to inhibiting contamination of felts of a papermaking system. More particularly, the present invention relates to a press felt conditioner which controls contamination by wet strength resins. In several types of papermaking processes, water soluble wet strength resins are added to the pulp furnish to increase the end use wet strength properties of the paper products. Items such as paper towels, napkins and tissues as well as other specialty paper grades are formed from pulp furnish which includes wet strength resins. These wet strength resins enhance the strength of the end product when wet. Wet strength resins which allow the end product paper to retain more than 15% and up to 50% of its dry strength when wet are well known in the papermaking art. Various types of wet strength resins include ureaformaldehyde, melamine-formaldehyde, polyacrylamide, poly(aminoamide)-epichlorohydrin resins and their complex derivatives which are employed as pulp furnish components. The poly(aminoamide)-epichlorohydrin (PAE) type resins have become the most commercially important thermosetting resins and dominate the current paper wet strength resin market. PAE resins are water soluble cationic polymers which are typically added to the pulp furnish at an intermediate degree of polymerization so that the final cure of the polymer occurs in the dryer section of the paper machine. PAE resins are used extensively because they are neutral to alkaline curing, they impart permanent wet strength properties and they provide long shelf life. Also, because PAE resins are water soluble cationic polymers, they are effectively retained on anionic cellulosic fibers. By water soluble, it is meant that the resins are water soluble at the time they are added to the papermaking furnish. Subsequent events such as crosslinking can render the resins insoluble in water. Wet strength resins are generally believed to undergo crosslinking or other curing reaction after they have been deposited on, within, or among the papermaking fibers. The manufacture of paper typically involves the processing of a carefully prepared aqueous fiber suspension (the pulp furnish) containing chemical additives to produce a highly uniform dry paper. Three steps included in the typical paper process are sheet forming where the suspension is directed over a porous synthetic mesh or "wire"; sheet pressing, where a formed sheet is passed through presses covered with belt-like porous felts to extract retained water from the sheet and to transfer the delicate sheet to the next final step of paper drying, commonly known as "yankee drying" in the case of tissue and towel grade papers. Press felts commonly circulate continuously in a belt-like fashion between a sheet contact stage and a return stage. During the sheet contact stage, water along with other contaminants and additives is drawn from the sheet, usually with the aid of press rolls and/or a vacuum, into the pores of the felt and then subsequently removed from the felt. The quality of the aqueous fiber suspension used to produce the sheet is dependent upon many factors including the composition of any recycled fibers added to to the process as well as the additives used in the preparation of the paper furnish. Thus, a variety of dissolved or suspended materials can be introduced into the manufacturing process, including both organic and inorganic materials such as talc, rosin, pitch, lignin, wet strength resins, cationic or anionic retention aids, water treatment chemicals, fines, anionic trash resins, calcium carbonate, clay, kaolin, silicon dioxide, titanium dioxide, alum, hydrolized AKD and ASA size, starch coating from broke, binding resins, ink particles, toners, dyes, etc. The ultimate result of these well intended additives in the aqueous fiber suspension is that they tend to deposit in the fine pores of the porous felts if they don't become an integral part of the sheet and are not removed from the felt continuously by chemical and/or mechanical means. The presence of wet strength resins in the process system compounds the problem. When PAE resin is present in the system, it tends to crosslink with itself and size the press felt fibers and render the felt surface nonabsorbent over time. In this situation, serious machine runnability and quality problems occur, ultimately leading to significant production loss. This is particularly true in current operations where the press felts are made of a polyamide fiber (nylon with various variations in fiber size, base structure, density, porosity, surface treatment, etc.) which generally carries a negative surface charge and possesses a high affinity for PAE type wet strength resins. To control these problems related to PAE contaminated press felts, the felts have traditionally been mostly batch washed since few continuous felt conditioning chemicals are known to be effective. Batch cleaning products typically contain alkali, chelants, surfactant compositions and some solvents or in more severe cases, sodium hypochlorite solution is used alone. Even with these harsh and frequent batch wash treatments, PAE type wet strength resins along with other contaminants have been found difficult to remove. The use of sodium hypochlorite is relatively more effective for removing PAE resin but its detrimental effect on polyamide (nylon) fibers causes other problems such as loss of batt fibers from the felt (fiber shedding) and weakening of the felt's integrity, etc. leading to premature felt damage and short felt life. In addition, the use of chlorine based reagents is being limited in the pacer industry due to increased environmental and regulatory restrictions. Batch cleaning operations where the machine is shut down also result in significant production losses. Continuous felt conditioning chemical treatments based upon various nonionic or anionic surfactants, solvents, dispersants, etc. have been employed in the art. However, current continuous felt conditioning treatments have shown very limited efficacy toward controlling the PAE wet strength resin deposition in press felts. European Patent Specification No. EP-A-0 550 230 discloses the inhibition of deposits of polymerically flocculated particulate material in press felts of a papermaking system by applying to the felts fatty acid imidazolines. United Stated Patent No. 3,895,622 discloses a papermaking machine press felt conditioning treatment involving applying to the felt an inhibiting amount of a conditioner comprising a relatively low molecular weight organic anionic polymer and at least one hydrophilic, nonionic or anionic surfactant. The present inventors have discovered that several functionally similar members of the class: alkylamidopropyldimethylamine, ethoxylated nonylphenols having greater than about 30 moles of ethoxylation, and sodium n-hexadecyl diphenyloxide disulfonate are very effective, when employed as continuous felt conditioning agents, at inhibiting PAE wet strength resin contaminant deposit in press felts. The materials of the present invention also enhance the water absorbing and permeability properties of the press felts. According to the present invention, there is provided the use, as an inhibitor, applied to a press felt of a papermaking system, of deposition of poly(amido-amine)-epichlorohydrin type resins in said press felt, of an effective inhibiting amount of a press felt conditioner selected from the group: ethoxylated nonylphenol having more than about 30 moles of ethoxylation; sodium n-hexadecyl diphenyloxide disulfonate; and alkylamidopropyldimethylamines of the general formula: wherein R is a saturated, unsaturated, monounsaturated or branched alkyl hydrophobe radical having a carbon chain length of about 18. The press felt conditioning agents of the present invention are preferably applied by metering into one or more fresh water showers directed onto a press felt between the press nip and the vacuum or uhle box utilized for dewatering the felt. The conditioners are effective at inhibiting the deposition of PAE wet strength resin contaminants in the press felts. It was discovered that alkylamidopropyldimethylamines having similar alkyl hydrophobe substituents are unexpectedly efficacious PAE type contaminant inhibitors. The alkyl hydrophobe substitutions can be saturated, unsaturated, monounsaturated or branched alkyl groups. Ethoxylated nonylphenol having greater than 30 moles of ethoxylation and sodium n-hexadecyl diphenyloxide disulfonate were also found to be effective PAE type contaminant inhibitors. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a process for inhibiting the deposition of PAE type contaminants in the felts in the press section of a papermaking system. The process of the present invention comprises treating the felts, typically in an aqueous spray or shower, with a felt conditioner. The felt conditioner of the present invention comprises an effective inhibiting amount of an ethoxylated nonylphenol having greater than 30 moles of ethoxylation, a sodium n-hexadecyl diphenyloxide disulfonate, an alkyl substituted amidopropyldimethylamine. The alkyl substituent is an alkyl hydrophobe radical which can be saturated, unsaturated, monounsaturated, or branched alkyl groups. Alkylamidopropyldimethylamines in accordance with the present invention are exemplified by the general structure. R is an alkyl hydrophobe radical with a preferred carbon chain length of C 18 . R can be saturated, unsaturated, mono unsaturated or a branched alkyl group. The alkylamidopropyldimethylamines are the preferred felt conditioners of the present invention. The press felt conditioners of the present invention are typically applied to the press felt in an aqueous shower. The conditioner is preferably metered into one or more fresh water showers directed onto a press felt between the press nip and the vacuum or uhle box utilized for dewatering the felts. The required amount or concentration of conditioner will depend on, among other things, the volume of shower water employed, the production rate, the amount of PAE resins used, etc. Generally, the total concentration of the conditioning agent of the present invention may range from about 15 to 1,200 parts per million of the aqueous medium. Preferably, the conditioning agent is added at concentrations of from about 75 to about 350 parts per million of the aqueous showering medium. The practice of the present invention will be illustrated in the following examples. These examples are included as illustrations only and should not be construed as limiting the scope of the present invention. EXAMPLES The following examples demonstrate the unexpected efficacy of the felt conditioning treatment of the present invention. The data was obtained utilizing a continuous felt conditioning test apparatus and a simulated synthetic contaminant test system. The synthetic contaminant test system contained PAE wet strength resin, inorganic fillers. wood pitch and a hemicellulose substitute. The continuous felt conditioning testing incorporates a clean (unused) tissue grade press felt of known initial weight and air permeability placed on a heavy mesh support screen through which the treated and untreated contaminant solutions are pressed. After continuous conditioning testing, the sample is dried and acclimated at ambient temperature prior to retesting for percent weight gain and air permeability loss. Lower percent weight gain (less deposition) and lower numbers for permeability loss are indicative of a better performance. The simulated synthetic contaminant used in the testing is set out in Table 1. Ingredient Concentration in Water (ppm) Dried PAE Resin (Kymene Plus) 400 Clay 150 Talc 75 TiO 2 25 Fatty Ester Pitch 100 Carboxymethyl Cellulose (CMC) 75 Kymene Plus used in the simulated contaminant composition is a commercial PAE type wet strength resin available from Hercules, Inc., Wilmington, DE. Table 2 summarizes the test results for a number of commercially available surfactants, dispersants, polymers, reagents, and solvents studied in the testing. These commercially available materials are employed in the art for continuous or intermittent press felt conditioning of paper machine press felts. All tests were conducted at 150 ppm treatment concentration, pH 7.0 and at room temperature. Table 2 summarizes the results of the testing. Conditioning Agent % Weight Gain of Test Felt % Porosity Loss of Test Felt Untreated Control 17.7 73.1 Oleamidopropyldimethylamine 2.7 34.5 Surfactants Ethoxylated Nonylphenol (n=9.5) 10.4 47.9 Ethoxylated Nonylphenol (n=12) 11.8 54.8 Ethoxylated Nonylphenol (n=30) 6.8 49.2 Ethoxylated Nonylphenol (n=100) 8.0 46.9 Ethoxylated Dinonylphenol 12.7 56.3 Linear Alcohol Ethoxylate Complex Phosphate Ester 11.4 69.9 Nonylphenol Ethoxylate Complex Phosphate Ester 21.6 75.5 Phenol Ethoxylate Complex Phosphate Ester 17.5 78.4 Primary Alcohol Ethoxylate 18.6 74.7 Primary Alcohol Ethoxylate 17.0 87.0 Secondary Alcohol Ethoxylate 16.0 71.2 Branched Unidecyloxoalcohol Ethoxylate 20.6 75.5 Branched Tridecyl Alcohol Ethoxylate 16.8 73.4 Alkyl Polyglucoside 21.6 65.0 Alkyl Betaine 12.9 63.3 Alkyl Sultaine 19.1 79.3 Sodium Diisosulfosuccinate 23.5 73.6 Ethoxylated Alcohol Ether Sulfate 18.7 80.7 Tris Alkylamido Triquatinary 19.3 83.6 Alkylamidopropyl Morpholine 15.2 74.1 Sodium n-hexadecyl Diphenyloxide Disulfonate 6.8 54.6 Sodium n-dodecyl Diphenyloxide Disulfonate 12.3 65.8 Sodium n-decyl Diphenyloxide Disulfonate 23.9 73.0 Sodium N-methyl-N-oleoyl Taurate 20.8 69.5 Sodium 2-Ethylehexyl Sulfate 17.9 81.1 Alkyl Pyrrolidone 17.3 80.4 (Propylene/Ethylene oxide) Block Copolymer 8.9 47.4 Dispersants Polymethyl Napthalene Sulfonate (low MW) 23.1 62.2 Polymethyl Napthalene Sulfonate (high MW) 13.2 73.7 Sodium Lignosulfate 15.4 60.7 Polymers Polyquatinary Ammonium Chloride 14.8 53.8 Polyvinyl Alcohol 14.0 82.9 Polyvinyl Pyrrolidone 15.7 77.9 Polyacrylic Acid 16.5 76.3 Poly(Methyl Vinyl Ether/Maleic Acid) 22.4 85.3 Solvents Aliphatic Solvent 21.8 80.9 Branched Alkyl Diamine 17.9 75.7 Reagents Aluminum Sulfate 23.5 75.5 Triethanol Amine 17.6 70.2 The results summarized in Table 2 clearly show that the oleyl amidazoline and oleamidopropyldimethylamine are unexpectedly efficacious at controlling the percent weight gain and loss of porosity. Additional testing under the same conditions at pHs of 6.5 and 8.0 showed similar efficacy. In addition to Kymene Plus based PAE wet strength resins, several other "Kymene" series PAE wet strength resins were tested to demonstrate the effectiveness of the present invention. Table 4 summarizes the results. Kymene Type Control C18 Alkylamidopropyl Dimethylamine %Wt. Gain % Porosity Loss %Wt. Gain % Porosity Loss Kymene Plus 17.7 73.0* 2.7 34.5 Kymene 557 22.1 65.6 3.4 38.5 Kymene 736 14.1 59.0 3.0 15.8 Kymene 218 18.0 69.6 6.5 50.3 The data of Table 4 shows that the treatment of the present invention is effective in controlling the deposition of a number of PAE type wet strength resins in a press felt. While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of the invention will be obvious to those skilled in the art. The appended claims and this invention should be construed to cover all such obvious forms and modifications which are within the scope of the present invention.

Claims: The use of an effective inhibiting amount of a press felt conditioner, applied to a press felt of a papermaking system, as an inhibitor against the deposition of poly(amido-amine)-epichlorhydrin type resins in said press felt, the conditioner being selected from the group: ethoxylated nonylphenol having more than about 30 moles of ethoxylation; sodium n-hexadecyl diphenyloxide disulfonate; and alkylamidopropyldimethylamines of the general formula: wherein R is saturated, unsaturated, monounsaturated or branched alkyl hydrophobe radical having a carbon chain length of about 18. A use as claimed in claim 1, wherein the pH of the system is from about 6.5 to about 8.0. A use as claimed in claim 1 or 2, wherein said press felt is conditioned by showering with an aqueous medium including said felt conditioner. A use as claimed in claim 3, wherein said press felt conditioner is present in an amount of from about 15 to about 1,200 parts per million parts said aqueous medium. A use as claimed in any one of the preceding claims, wherein the press felt conditioner is an alkylamidopropyldimethylamine of the general formula: wherein R is an saturated, unsaturated, monounsaturated or branched alkyl hydrophobe radical having a carbon chain length of about 18.

Inventors: CURHAM KEVIN DONALD, KHAN ABDUL QAVI, CURHAM, KEVIN DONALD, KHAN, ABDUL QAVI
Applicants: BETZ EUROP INC, BETZDEARBORN EUROPE, INC.
Application year: 1994
Main classification: D21H21
IPC codes: D06M13, D21H21, D21F1, D06M15